(+)-7-[4-(4-fluorophenyl)-6-isopropyl-2-(methansulfonyl-methyl-amino)-pyrimidin-5-yl]-(3R,5S)-dihydroxy-hept-6-enoic acid (rosuvastatin) of the Formula (I) is a known compound which has been disclosed for the first time in European Patent No. 521471 in the form of the free acid and as certain pharmaceutically acceptable salts, e.g. rosuvastatin calcium salt of the Formula (IV)
as well as ammonium salts thereof.
Rosuvastatin zinc (2:1) salt of the Formula (V)
has been disclosed in Published Hungarian Patent Application P0600293 and in Published International Patent Application WO 2007119085.
According to the method of preparation disclosed in European Patent No. 521471, preparation of a rosuvastatin salt is carried out by saponifying a rosuvastatin ester of the general Formula (II) and if desired, the rosuvastatin salt thus obtained is transformed into rosuvastatin acid and either the directly obtained rosuvastatin salt or rosuvastatin free acid of the Formula (I) is transformed into a pharmaceutically acceptable salt, preferably into the calcium salt of the Formula (IV).
Rosuvastatin is an easily decomposing, light-sensitive compound, therefore further methods have been developed with the aim to obtain rosuvastatin in higher purity.
The chemical purity of pharmaceutically active ingredients is regulated by strict official norms issued by health authorities. Thus, according to the ICH Guidelines—even in the case of impurities with known chemical structure—the maximum limit concentration thereof is fixed at 0.1% in a pharmaceutically active ingredient.
Salts of rosuvastatin formed with amines are widely used during the manufacture of rosuvastatin salts used in the production of finished dosage forms. According to the state of the art, such salts of rosuvastatin formed with amines are transformed into a pharmaceutically acceptable alkali metal or alkali earth metal salts of rosuvastatin by setting the amine free from the salt using a stronger base and the thus obtained salt, which is usually an alkali metal salt, is subsequently transformed into the salt form used as active ingredient in the finished dosage form.
Published International Patent Application WO 01060804 is related to crystalline ammonium, methylammonium, ethylammonium, diethanolammonium, tris(hydroxymethyl)-methylammonium, benzylammonium or 4-methoxybenzyl-ammonium salts, which are transformed into amorphous rosuvastatin calcium salt by converting a rosuvastatin ammonium salt mentioned above into rosuvastatin sodium salt using aqueous sodium hydroxide solution, which is converted in the second step into rosuvastatin calcium (2:1) salt of the Formula (IV), and filtering the product from the aqueous solution. The purity of the product has not been disclosed.
Published International Patent Application WO 2008038132 discloses salts of rosuvastatin formed with diamines. Among the salts, only the dibenzylethylenediamine salt is characterized by X-ray diffraction data. The salts are prepared starting from rosuvastatin of the Formula (I) or rosuvastatin sodium salt.
Published International Patent Application WO 2008067440 discloses a method for the preparation of rosuvastatin calcium salt of the Formula (IV) starting from the dehydroabiethylamine salt of rosuvastatin through rosuvastatin sodium salt, in an aqueous solvent. The purity of the rosuvastatin calcium salt disclosed in an example is 99.80% as measured by high-performance liquid chromatography (HPLC) and contains the diastereomer impurity in 0.14% concentration, which is very close to the limit concentration (0.15%).
Direct transformation of several rosuvastatin ammonium salts into rosuvastatin calcium salt (wherein no rosuvastatin sodium salt is produced) has been disclosed in Published International Patent Applications WO 2004014872 and WO 2006136407. The reactions are carried out in an aqueous solvent.
Published International Patent Application WO 2004014872 is related to a method for preparation of rosuvastatin calcium salt with specific operating parameters, which results in the enhancement of the filtering efficiency during the isolation of the salt precipitating from water. In the method, rosuvastatin calcium salt of the Formula (IV) is obtained from certain water-soluble rosuvastatin ammonium salts (ammonium, tris-hydroxymethyl-methylammonium, methylammonium salts).
Published International Patent Application WO 2005077916 is related to crystalline and amorphous rosuvastatin cyclohexyl-, dicyclohexyl-, isopropyl-, diisopropyl- and (S)-1-methylbenzyl-ammonium salts. These salts are prepared by reacting a rosuvastatin ester, rosuvastatin or rosuvastatin lactone with the corresponding amine and purified by recrystallization. However, no method parameters have been disclosed or exemplified for the method using ester or lactone as starting materials, therefore neither the yield of the method nor the quality of the product can not be determined. The salts mentioned above are transformed into rosuvastatin calcium of the Formula (IV) by converting first the rosuvastatin ammonium salt into rosuvastatin lactone of the Formula (VI)
which is subsequently converted into the sodium salt and by reacting with a calcium ion source in aqueous medium and filtering, amorphous rosuvastatin calcium salt having its purity in excess of 99.5% (as determined by HPLC) is obtained. Nevertheless, the concentration of the diastereomeric impurity is high: using the method disclosed in the above-mentioned application, the concentration of the diastereomeric impurity can not be decreased below approx. 0.25%. Such an active ingredient, however, does not comply with internationally accepted ICH Guidelines, since the limit concentration for impurities having known chemical structure is thereby set to 0.1% for each impurity. A further disadvantage of the method is that the ammonium salt is transformed into the final product through further intermediates in multiple steps.
In Published International Patent Application WO 2005051921, a method for purification of rosuvastatin calcium salt through the crystalline isopropyl- or cyclohexylammonium salt has been disclosed. Rosuvastatin calcium salt is first transformed into rosuvastatin of the Formula (I), which is thereafter converted into rosuvastatin isopropyl- or cyclohexylammonium salt using ethylacetate as solvent. Subsequently the ammonium salt is transformed into sodium salt in aqueous medium and the sodium salt is transformed into rosuvastatin calcium salt (2:1) of the Formula (I) in an aqueous solvent. The yield of the reaction is 73.6% without disclosing the purity.
There are several methods in the state of the art relating to the hydrolysis of rosuvastatin esters with bases. In most cases, esters are saponified with aqueous alkali metal hydroxides yielding rosuvastatin alkali metal salts. Ammonium salts are prepared by converting a rosuvastatin alkali metal or alkali earth metal salt into rosuvastatin acid of the Formula (I) which is subsequently reacted with an amine yielding ammonium salt.
Thus, for example, hydrolysis of rosuvastatin methylester of the Formula (IIa) with aqueous sodium hydroxide solution has been disclosed in Published International Patent Applications WO 2003097614, WO 2004052867 and WO 2006017357. According to Published International Patent Application WO 2007000121, hydrolysis of rosuvastatin methylester of the Formula (IIa) is carried out using lithium hydroxide.